Theridion grallator, also known as the Hawaiian happy-face spider, is a spider in the family Theridiidae that resides on the Hawaiian Islands. T. grallator gets its vernacular name of "Hawaiian happy-face spider" from the unique patterns superimposed on its abdomen, specifically those that resemble a human smiling face. T. grallator is particularly notable because of its wide range of polymorphisms that may be studied to allow a better understanding of evolutionary mechanisms. In addition to the variety of color polymorphisms present, T. grallator demonstrates the interesting quality of diet-induced color change, in which its appearance temporarily changes as it metabolizes various food items. Description T. grallator is a small spider with a body size less than 5 millimeters long. It has characteristically long and slender legs and a translucent yellow body. These distinctly long legs lead T. grallator to have the most divergent bodily morphology out of all the members of its clade. This unique characteristic occurred as a result of an ecological or behavioral shift. Its abdomen is often pale, translucent yellow, and can also contain a variety of red, white, and/or black superimposed patterns. Certain morphs have a pattern resembling a smiley face or a grinning clown face on their yellow body. These patterns differ from island to island. Some lack abdominal markings altogether. Abdominal color changes from translucent yellow to green or orange, depending on diet. The variety of polymorphisms present in T. grallator allows an evolutionary benefit to evade predation. Spiders with depigmentation or polymorphic colors and patterns can avoid predation by birds that use a search image when scanning for prey. A search image may be a particularly abundant color morph, and predators will use this as an identification of possible prey. Color morphs A key characteristic of T. grallator is the presence of a large variety of abdominal color morphs. The ratio of unpatterned to patterned morphs is relatively constant throughout the year. It is also constant between and within populations regardless of climate and elevation, indicating some form of selection acting to maintain these proportions. Although across all of the Hawaiian islands, there is a similar frequency of the discrete morphs, there are different genetic bases for these morphs between islands. The various morphs are assigned to a series of broad categories that characterize the abdominal color and/or its patterned patches. These categories include: Yellow, Red front, Red back, Red front and back,